1. Field of the Invention
The present invention relates to a hybrid super capacitor using a composite electrode, and more particularly, to a hybrid super capacitor using a complex electrode that may enhance equivalent series resistance using a carbon nanotube chain.
2. Description of the Related Art
An electrochemical double layer capacitor (EDLC) may accumulate electric energy using an aspect that charges are accumulated in an electrochemical double layer formed in an interface between a solid electrode and an electrolyte. The EDLC has a relatively short charging time and has a relatively high output density of 1000 W/kg to 2000 W/kg. In addition, a cycle lifespan characteristic is semi-permanent which is long. The ELDC has a characteristic that a charging and discharging reaction occurs only in the interface, that is, the electrochemical double layer between the electrode and the electrolyte. Since such reaction is limited to the surface, the energy density to be stored may be 1 Wh/kg to 10 Wh/kg which is relatively low.
The EDLC includes an electrode, a separating film, an electrolyte, and a case. A most important element in the EDLC is an electrode material used for the electrode. Since the electrode material needs to have a great electric conductivity and specific surface, and to be electrochemically stable, activated carbon or activated fiber is mostly widely used.
Even though the EDLC may employ a method of increasing a drive voltage in order to increase the energy density, increasing of the drive voltage is limited to the range in which dissolution of electrolyte does not occur and thus, there are some constraints. To solve this, when an activated carbon is used as the electrode material, a charging capacity may increase by increasing pores on the surface of the activated carbon, thereby enhancing the energy density. However, there is some constraint in increasing the pores on the surface of the activated carbon.
A hybrid super capacitor has been developed to enhance the aforementioned energy density of the EDLC. The hybrid super capacitor has enhanced the energy density by employing an activated carbon for an anode and employing a lithium titanium oxide (LTO, Li4Ti5O12) for a cathode. The lithium titanium oxide has a characteristic that an electric potential is relatively high with respect to lithium and a reactive material with electrolyte or lithium is not extracted in the interface and thus, the stability and a low temperature characteristic is excellent.
A conventional hybrid super capacitor has enhanced the energy density by employing an activated carbon for an anode and employing a lithium titanium oxide for a cathode. However, since the lithium titanium oxide has a relatively high electric potential with respect to lithium, resistance may increase when the lithium titanium oxide is combined with the activated carbon. As described above, when resistance of an electrode material increases, equivalent series resistance (ESR) of the hybrid super capacitor may also increase, thereby deteriorating the output density and lifespan of the hybrid super capacitor.